Abstract The fractions and polysaccharides from Sasa veitchii were evaluated for their preventive effects on influenza A virus (IFV-A) infection. In IFV-A infected mice, the high-molecular portion (SH) of hot-water extract from S. veitchii significantly reduced virus yields in lung and bronchoalveolar lavage fluid (BALF) and increased in IFV-A-specific secretory IgA in BALF and intestine samples, and neutralizing antibody titers in BALFs and sera. Separation of SH by combination with ion-exchange column and gel filtration yielded six purified polysaccharides. Among them, SH2A1B1 with molecular weight of 29.7 kDa was found to reduce virus yields in lung as well as BALF in IFV-A-infected mice. A significant increase in the production of neutralizing antibody was also observed in BALFs on day 15 post-infection. Furthermore, significant enhancement of nitrite oxide production in RAW 264.7 cells was observed. These results suggest that the fractions from S. veitchii and SH2A1B1 could provide useful materials for prevention of IFV-A infection.